1. Field of the Invention
This invention relates to a method and apparatus for the manufacture of fibrous casings.
2. Description of the Prior Art
In the preparation of sausages by meat packers, a sausage emulsion is inserted into a natural or synthetic sausage casing which is subsequently tied off at each end and cooked. One type of synthetic casing provided to the trade is known as fibrous casing. Fibrous casing is composed of cellulosic fibers, generally in the form of a paper, which are impregnated and held together by regenerated cellulose. The paper which is used is usually a saturating tissue, preferably a long fiber hemp paper, which is formed into a tube and is impregnated with viscose solution. After the interstices of the paper have been filled with viscose solution and a coating of the solution is formed thereon, the tube is subjected to a coagulating bath to regenerate cellulose within and upon the paper. The dried product is a paper reinforced regenerated cellulose casing having relatively high strength and relatively low stretch.
When the above-disclosed procedure for the manufacture of fibrous casing is followed, difficulties are encountered during the step of viscose impregnation of the paper. In the procedure for impregnating the paper tube with viscose, a paper sheet formed into the shape of a tube proceeds downwardly over a hollow mandrel which acts to maintain the paper in tubular form during the viscose impregnation. The mandrel is further provided with a plurality of metal slip rings which function to keep the viscose impregnated paper tube from binding against the outside wall of the mandrel as the tube moves downwardly. After passage of the viscose impregnated tube over the mandrel, the tube enters a coagulating bath wherein the viscose on the outer surface of the tube is coagulated and regenerated. Regeneration of viscose on the interior surface of the tube is accomplished by feeding coagulation liquid to the interior tube portion present at the bottom of the mandrel. Thereafter, the tube is removed from the bath and washed and dried to obtain the desired fibrous casing.
During the regeneration of cellulose on the tube interior, spent coagulation liquid accumulated within the lower interior portion of the tube is withdrawn therefrom by means of a vacuum line which extends through the entire length of the hollow mandrel and into the area of the tube interior where the spent liquid has accumulated. The imposition of the vacuum creates a pressure differential which acts on the spent liquid to cause it to flow upwardly in the vacuum line. The imposition of the vacuum to effect removal of the spent liquid has also been found to create a zone of negative pressure in the space between the inner surface of the tube and the outer surface of the mandrel as the air in the space is removed therefrom and drawn into the liquid being withdrawn from the tube. The negative pressure created between the inner tube surface and outer mandrel surface causes the tube to be drawn into wiping contact with the rings mounted on the mandrel. Contact of the internal wall of the wet viscose-coated tube with the rings causes a portion of the viscose coated on the tube wall to be scraped therefrom and collected on the rings. After continued passage of the wet impregnated tubes over the rings under these conditions, there results an excessive accumulation of viscose which eventually breaks loose from the rings and deposits on the internal surfaces of the tube which result in "viscose spots" in the finished casing, i.e., areas of uneven coating. Poor yields of casing also result as the accumulation of viscose on the rings creates a drag force on the descending tube which causes the weakly sealed wet casing to rupture and tear apart.